If the velocity of the object changes from 2 cm / sec to 14 cm / sec in 3 seconds, then at what average rate is the velocity changing?

Starting from rest, a ball rolls down a constant incline.  It requires 9.8 seconds to roll the 84 centimeter length of the incline.

An object which accelerates uniformly from rest will attain a final velocity which is double its average velocity.

In 15 seconds, a bicycle accelerating uniformly from rest covers a distance of 148 meters.  At what average rate is its velocity changing?